In the production and finishing of metal workpieces, for example elongate steel slabs, billets, and bar stock, the steel is conditioned or surface finished by creating relative motion between the steel workpiece and a scarfing apparatus having at least one scarfing unit positioned along the top, bottom, or side surfaces of the workpiece to eliminate surface defects such as cracks, seams, slag inclusions, surface oxides, and mechanical defects resulting from the rolling or casting process, for example. One known type of such a scarfing apparatus includes top, bottom, and opposed side scarfing units that are mounted across the width and end portions of the workpiece to concurrently scarf each of the sides of the workpiece as it is passed through the scarfing apparatus and between the scarfing units so provided.
The top, side, and bottom scarfing units of the scarfing apparatus each include a manifold and head assembly constructed and arranged to receive and distribute both oxygen and fuel gas to opposed upper and lower pre-heat blocks or block assemblies provided as a part of each such scarfing unit. The respective upper and lower pre-heat blocks are spaced from one another to define an oxygen scarfing slot therebetween, and through which a quantity of oxygen is passed under pressure and directed toward the workpiece to enable the thermochemical scarfing process to occur. The lower pre-heat block will typically include a fuel gas channel having a discharge opening positioned adjacent the oxygen slot formed by the upper and lower pre-heat blocks for discharging a fuel gas adjacent the oxygen flow for the purpose of maintaining the oxidation reaction on the surface of the workpiece, and for also shielding the oxygen flow from aspiration, i.e., from mixing with ambient air, which tends to diminish the effectiveness of the thermochemical scarfing process.
One example of such a known type of lower pre-heat block is disclosed in U. S. Pat. No. 2,838,431 to Allmang et al., in which the pre-heat block is disclosed as being of one piece construction and includes a spaced series of fuel gas outlets extending across the width of the front face of the block. The fuel gas is delivered to the inlet ports through a number of laterally spaced fuel gas lines which extend from a rear face of the block to a transverse internal bore positioned just behind, and in communication with the inner ends of the outlet ports. An elongate dividing rod, or bar, comprising a number of spaced transverse discs is positioned within the bore so as to divide the bore into a series of uniform gas distribution chambers. The ends of the bore are closed with end seals in known fashion.
Although the fuel gas outlet ports defined in the front face of the lower pre-heat block of Allmang, et al. were an improvement over the then-known scarfing machines, in that the fuel gas ports were closely spaced with respect to one another in the effort to prevent outside air from aspirating with the oxidizing gas stream, the problem still remained that outside air would tend to be drawn toward and between the fuel gas outlet ports such that outside air would aspirate with the oxidizing gas flow.
As known to those of skill in the art, the shielding of the sheet-like oxygen stream, or oxidizing gas flow created when oxygen is passed between the upper and lower pre-heat blocks is most critical in producing a smooth scarfed surface on the workpiece being scarfed as any variation or inconsistency in the lower pre-heat block fuel gas flame can cause a variation in the scarfed surface. Any such variation can lead to non-uniform metal removal, with ridges and valleys being the result, such that the scarfing depth must be increased in order that these ridges or valleys be removed, i.e., a sufficient quantity of the surface of the object must be removed to provide for the removal of all such surface defects which pre-existed the scarfing process, as well as those which may have been caused by the scarfing process. As a result, the scarfing apparatus of Allmang, et al. and others similarly constructed, led to the removal of excess metal, causing otherwise satisfactory metal to be removed which increases yield loss rates during the workpiece finishing process.
The scarfing apparatus of Allmang et al. was improved upon in U.S. Pat. No. 3,231,431 to Allmang by adding an elongate baffle strip of an approximate one-half (1/2) inch length positioned approximately one-quarter (1/4) inch below the oxygen slot to prevent the aspiration of ambient air into the oxygen stream, as disclosed in Column 2, Lines 34-72, and Column 3, Lines 1-13 thereof. As stated in Column 2, Lines 61-65 of Allmang, it was believed that a confining action caused by the baffle strips on both sides of the oxygen-fuel mixture prevented atmospheric air from aspirating with the oxygen at a point adjacent to each row of pre-heat (gas outlet) ports.
Although the patent to Allmang represented an improvement in the art, the need still existed for an improved scarfing apparatus which would more consistently produce a smooth surfaced scarfed metal workpiece. It was to the attainment of this object that the lower pre-heat block assembly of Showalter, et al. disclosed in U.S. Pat. No. 5,497,976 was developed. Showalter attained a smooth surface scarf by providing a lower pre-heat block assembly for use in a thermochemical scarfing apparatus which included an improved fuel gas delivery system for delivering a stream of fuel gas uniformly across the full width of the metal workpiece, and which shielded the oxidizing gas flow to ensure that the peaks and valleys resulting from the use of the earlier known scarfing devices were minimized. This was accomplished by providing a two-piece lower pre-heat block assembly having a base member or block, and an extension releasedly fastened thereto in engaging and overlying relationship on the front face of the block. An elongate gas discharge slot was machined into the extension, which slot communicated with a spaced series of gas discharge ports defined within and extending longitudinally across the front face of the block. The extension also included internal baffles for inducing turbulence in the fuel gas flow to ensure complete mixing of the fuel gas, such that the fuel gas would be emitted through the gas discharge slot as a uniform flow across the face of the extension.
The lower pre-heat block assembly of Showalter et al. represented a significant advance in the art, but it required that a two-piece lower pre-heat block assembly be manufactured in which a precisely machined slot is required within the extension, and which also required the use of internal baffles for inducing turbulence in the fuel gas flow to ensure that the fuel gas is distributed uniformly across the width of the extension in order to prevent ambient air from aspirating with the oxidizing/oxygen gas flow as it is passed between the upper and lower pre-heat block assemblies, and directed toward the metal object or workpiece to be thermochemically scarfed.
What is needed, therefore, but seemingly unavailable in the art is an improved lower pre-heat block assembly for use with a thermochemical scarfing apparatus which is simple in design and manufacture, and which will ensure that a sheet-like fuel gas flow is produced for shielding the oxidizing gas flow.
In the lower pre-heat block assembly of Showalter et al., the disclosed gas discharge slot is provided within an otherwise conventional extension having a baffle similar to that disclosed in U.S. Pat. No. 3,231,431 to Allmang, such that should the fuel gas discharge slot became plugged or obstructed at any point along its length, the probability exists that ambient air will be allowed to aspirate with the oxidizing gas flow, which may lead to the formation of peaks and valleys during the metal scarfing process. What is needed, therefore, is an improved lower pre-heat block assembly for use with a scarfing apparatus in which a gas discharge outlet which is less likely to become obstructed is defined within the modular base or block, and with which the extension can be placed in engaging and overlying position such that it defines a gas discharge orifice of a desired size in the face of the block for simplifying the manufacture of the lower pre-heat block assembly, and for allowing the fuel gas to be distributed evenly across the width of the lower block assembly so that the lower block will perform satisfactorily even if there may be plugs or obstructions in the gas discharge outlets to shield the oxidizing gas flow from ambient air during the scarfing process.
Lastly, although the baffle of the patent to Allmang proved useful in minimizing the aspiration of ambient air within the oxidizing gas flow, this problem still persists, even with the improved lower pre-heat block assembly of Showalter et al. Accordingly, what is needed is an improved lower pre-heat block assembly for use with a thermochemical scarfing apparatus which is constructed to utilize the oxidizing gas flow as it is passed over the lower pre-heat block assembly to pneumatically compress, or squeeze, the fuel gas between the oxidizing gas flow and the lower pre-heat block assembly such that the fuel gas is uniformly distributed across the width of the lower pre-heat block assembly, and for forming a sheet-like fuel gas flow which shields and adjoins the oxidizing gas flow as it is continues on toward the metal workpiece to be scarfed so as to minimize the likelihood that peaks and valleys will be formed during the scarfing process, and to improve production yields during the metal finishing process.